1. Field of the Invention
The present invention relates generally to a laser which comprises a mode control structure and, more particularly, to a vertical cavity surface emitting laser that is provided with an internal structure proximate one of its mirror structures that comprises different thicknesses that result in selective lasing locations by the laser.
2. Description of the Prior Art
Vertical cavity surface emitting lasers are well known to those skilled in the art. In IEEE Photonics Technology Letters, volume 4, no. 4 (April 1993) , an article titled "Transverse Mode Control of Vertical-Cavity Top-Surface-Emitting Lasers" by Morgan, Guth, Focht, Asom, Kojima, Rogers and Callis discusses transverse mode characteristics and the control for vertical cavity top surface emitting lasers. It also describes a spatial filtering concept for the control of VCSEL transverse modes allowing the achievement of over 1.5 mW single TEM transverse mode emission from continuous wave electrically excited VCSEL's. It also shows that, without spatial filtering, L-I and V-I kinks can be observed.
In IEEE Photonics Technology Letters, Volume 7, No. 5 (May 1995), an article entitled "200.degree. C., 96-nm Wavelength Range, Continuous-Wave Lasing from Unbonded GaAs MOVPE-Grown Vertical Surface-Emitting Lasers" by Morgan, Hibb-Brenner, Marta, Walterson, Bounnak, Kalweit and Lehman describes record temperature and wavelength range that was attained through the use of MOVPE-grown AlGaAs vertical cavity surface-emitting lasers. Unbonded continuous-wave lasing is achieved at temperatures up to 200.degree. C. from these top-emitting VCSEL's and operation over 96-nm wavelength regime near 850 nm is also achieved from the same nominal design. Temperature and wavelength insensitive operation is also demonstrated in this article and the threshold current is controlled to within a factor of 2 (2.5-5 mA) for a wavelength range exceeding 50 nm and to within 30 percent (5-10 mA) for a temperature range of 190.degree. C. at 870 nm.
In an article titled "Surface-emitting Microlasers for Photonic Switching and Interchip Connections", published in Optical Engineering, March 1990, Volume 29 No. 3 by Jewell, Scherer, McCall, Olsson, Harbison and Florez describes vertical cavity electrically pumped surface emitting microlasers which are formed on gallium arsenide substrates at densities greater than two million per square centimeter. Two wafers were grown with indium gallium arsenide active material composing three quantum wells, 80 angstroms thick, in one and a single quantum well 100 angstroms thick in the other. Lasing was seen in devices as small as 1.5 micrometers diameter with less than 0.05 micrometers cube active material. Single quantum well microlasers 5.times.5 micrometer square had room temperature current thresholds as low as 1.5 milliampere with 983 nanometers output wavelength. Ten-by-ten micrometer square single quantum well microlasers were modulated by a pseudorandom bit generator at one Gb/s with less than 10.sup.-10 bit error rate. Pulsed output &gt;170 milliwatt was obtained from a 100 micrometer square device. The laser output passes through a nominally transparent substrate and out of its back side, a configuration well suited for micro optic integration and photonic switching and interchip connections.
In SPIE (Society of Photo-Optical Instrumentation Engineers) Volume 1562 (1991), an article titled "Devices for Optical processing" by Morgan, Chirovsky, Focht, Guth, Asom, Leibenguth, Robinson, Lee and Jewell reports on batch processed, totally planar, vertical cavity top surface emitting gallium arsenide/aluminum gallium arsenide laser devices and arrays. Different size devices are studied experimentally. The article describes the measurement of continuous wave threshold currents as low as 1.7 milliamperes and output powers greater than 3.7 milliwatts at room temperature. The article also discusses interesting characteristics such as differential quantum efficiencies exceeding unity and multitransfers mode behavior. An array having a 64 by 1 individually accessed elements is characterized and shown to have uniform room temperature continuous wave operating characteristics in threshold currents approximately equal to 2.1 milliamperes with a wavelength of approximately 849.4 nanometers and an output power of approximately 0.5 milliwatts.
U.S. Pat. No. 5,331,654, which issued to Jewell et al on Jul. 19, 1994, discloses a polarized surface emitting laser. It describes a vertical cavity surface emitting semiconductor diode laser having a monolithic and planar surface and having lateral anisotropy in order to control the polarization of the emitted light beam. The diode laser includes a body of a semiconductor material having an active region therein which is adapted to generate radiation and emit the radiation from a surface of the body, and a separate reflecting mirror at opposite sides of the active region with at least one of the mirrors being partially transparent to the generated light to allow the light generated in the active region to be emitted therethrough. The anisotropy may be provided by utilizing anisotropy in the atomic or molecular structure of the materials forming the laser or by anisotropic patterning or deliberate offset alignment in processing of the laser or through anisotropic structures in the laser cavity to control the polarization of the emitted beam. U.S. Pat. No. 5,331,654 is hereby explicitly incorporated by reference.
U.S. Pat. No. 5,351,256, which issued to Schneider et al on Sep. 27, 1994, describes an electrically injected visible vertical cavity surface emitting laser diode. Visible laser light output from an electrically injected vertical cavity surface emitting laser diode is enabled by the addition of phase matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise indium aluminum phosphide which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors. U.S. Pat. No. 5,351,256 is hereby explicitly incorporated by reference.
U.S. Pat. No. 5,031,187, which issued to Orenstein et al on Jul. 9, 1991, discloses a planar array of vertical cavities surface emitting lasers. The device comprises an active region having a quantum well region disposed between two Bragg reflector mirrors separated by a wavelength of the emitting laser. A large area of the structure is grown on a substrate and then laterally defined by implanting conducting reducing ions into the upper mirror in areas around the lasers. Thereby, the laterally defined laser array remains planar. Such an array can be made matrix addressable by growing the structure on a conducting layer overlying an insulating substrate. After growth of the vertical structure, an etch or further implantation divides the conducting layer into strips forming bottom column electrodes. Top row electrodes are deposited in the perpendicular direction over the laterally defined top mirror. U.S. Pat. No. 5,013,187 is hereby explicitly incorporated by reference.
U.S. Pat. No. 5,245,622, which issued to Jewell et al on Sep. 14, 1993, describes a vertical cavity surface emitting laser with intra-cavity structures. The intra-cavity structures allow the vertical cavity surface emitting laser to achieve low series resistance, high power efficiencies and TEM.sub.00 mode radiation. In one embodiment of the invention, a VCSEL comprises a laser cavity disposed between an upper and a lower mirror. The laser cavity comprises upper and lower spacer layers sandwiching an active region. A stratified electrode for conducting electrical current to the active region is disposed between the upper mirror and the upper spacer. The stratified electrode comprises a plurality of alternating high and low doped layers for achieving low series resistance without increasing the optical absorption. The VCSEL further comprises a current aperture as a disc shaped region formed in the stratified electrode for surpressing higher mode radiation. The current aperture is formed by reducing or eliminating the conductivity of the annular surrounding regions. In another embodiment, a metal contact layer having an optical aperture is formed within the upper mirror of the VCSEL. The optical aperture blocks the optical field in such a manner that it eliminates higher transverse mode lasing. U.S. Pat. No. 5,245,622 is hereby explicitly incorporated by reference.
U.S. Pat. No. 5,359,447, which issued to Hahn et al on Oct. 25, 1994, discloses an optical communication with vertical cavity surface emitting laser operating in multiple transverse modes. The communication system uses a relatively large area of vertical cavity surface emitting laser. The laser has an opening larger than approximately 8 micrometers and is coupled to a multimode optical fiber. The laser is driven into multiple transverse mode operation, which includes multiple filamentation as well as operation in a single cavity. U.S. Pat. No. 5,359,447 is hereby explicitly incorporated by reference.
U.S. Pat. No. 5,237,581, which issued to Asada et al on Aug. 17, 1993, describes a semiconductor multilayer reflector and a light emitting device. The reflector includes a plurality of first quarter wavelength layers each having a high refractive index, a plurality of second quarter wavelength layers each having a low refractive index and high concentration impurity doping regions. The first and second layers are piled up alternately and each of the doping regions is formed at a heterointerface between the first and second layers. In this structure, the width and height of the potential barrier at the heterointerface becomes small so that tunnel current flowing through the multilayer reflector is increased. U.S. Pat. No. 5,237,581 is hereby explicitly incorporated by reference.
U.S. Pat. No. 5,115,442, which issued to Lee et al on May 19, 1992, discloses a top emitting surface emitting laser structure. Lasers of this type depend upon emission through apertured top surface electrodes. Biasing current, accordingly peripheral to the laser is introduced, follows the path which comes to confluent within the active region to effectively attain lasing threshold. The path is the consequence of a buried region of increasing resistance which encircles the laser at or above the active region. The buried region is produced by ion implantation-induced damage with ion energy magnitude and spectrum chosen to produce an appropriate resistance gradient integrated, as well as discrete, laser are contemplated by the patent. U.S. Pat. No. 5,115,442 is hereby explicitly incorporated by reference.
U.S. Pat. No. 5,258,990, which issued to Olbright et al on Nov. 2, 1993, describes a visible light surface emitting semiconductor laser. The laser comprises a laser cavity sandwiched between two distributed Bragg reflectors. The laser cavity comprises a pair of spacer layers surrounding one or more active, optically emitting quantum well layers having a bandgap in the visible range which serves as the active optically emitting material of the device. The thickness of the laser cavity is defined as an integer multiplied by the wavelength and divided by twice the effective index of refraction of the cavity. Electrical pumping of the laser is achieved by heavily doping the bottom mirror and substrate to one conductivity type and heavily doping regions of the upper mirror with the opposite conductivity type to form a diode structure and applying a suitable voltage to the diode structure. Special embodiments of the invention for generating red, green and blue radiation are also described in this patent. U.S. Pat. No. 5,258,990 is hereby explicitly incorporated by reference.